01.07 Pitx2-Dependent Gene Regulatory Network in Left Atrial Cardiomyocytes Underlie Atrial Fibrillation

J. D. Steimle1, M. Park1, F. J. Grisanti Canozo1, S. Fang3, Z. A. Kadow1, T. T. Tran1, P. G. Swinton2, Y. Huang3, M. H. Samee1, J. F. Martin1,2 1Baylor College Of Medicine,Molecular Physiology And Biophysics,Houston, TX, USA 2Texas Heart Institute,Houston, TX, USA 3Institute of Biosciences and Technology, Texas A & M University,Center For Epigenetics & Disease Prevention,Houston, TX, USA

Atrial fibrillation (AF) is the most common sustained arrhythmia in the United States with a 25% lifetime risk, and accounts for one-third of all cardiovascular diseases. Treatment and care associated with AF costs roughly $26 billion/year in the US alone and accounts for 10% of all Medicare spending. Debilitating complications linked to AF include heart failure and stroke. AF risk is resoundingly linked to common variation at the 4q25 locus, implicating cis-regulation of the transcription factor PITX2. PITX2 is expressed in left atrial (LA) myocardium where it has been implicated as underlying AF phenotypes in both patients and animal models. Although animal models of Pitx2 are susceptible to AF, the direct mechanisms regulated by Pitx2 remain undetermined. To understand the molecular drivers of AF, it is imperative to understand both the upstream regulation and downstream targets of PITX2.

Using Pitx2 gene-edited mice, we have performed a compendium of single nuclei RNA sequencing (snRNA-seq) and single nuclei assay for transposase-accessible chromatin sequencing (snATAC-seq) experiments to identify the role of Pitx2 in LA myocardium.

Using the snRNA-seq and snATAC-seq datasets, we identified differentially expressed genes with differentially accessible chromatin sites in both the cardiomyocyte and fibroblast populations of the LA. Among the genes in the LA cardiomyocytes, we see a reversal of left and right atrial expressed genes.

AF is a complex genetic disease with many underlying genetic and physiological variables. In this work, we have begun laying the groundwork to understand the direct molecular mechanisms governed by Pitx2 in the LA myocardium. In future work, we hope to investigate the cis-regulatory mechanisms of PITX2 at candidate loci identified in this study. Additionally, we plan to identify the molecular machinery by which PITX2 interacts to govern the cis-regulatory landscape of the LA myocardium in development and disease.